Field of the Invention
This invention concerns an implement detection arrangement for a tractor.
Description of Related Art
A hitch, such as a three-point linkage is one known arrangement used to attach implements to vehicle, for example an agricultural tractor for towing. The implement may be fully-mounted or semi-mounted whereby a semi-mounted implemented has a wheel engaging with the ground during soil operation while a fully-mounted implement puts all its load on the three-point linkage.
Three point linkages most frequently consist of two lower lifting arms to which an implement is attached. The lower lifting arms can be pivoted by respective hydraulic actuating cylinders to adjust the height position of the implement relative to the ground. Furthermore, these lower lifting arms may be manually adjusted in length and thus be adapted to the type of implement to be attached. An additional top link connects the implement to the tractor on a level above the lower lifting arms. This top link is used to pivot the implement about a horizontal transverse axis and is adjustable by means of a threaded connection, or a hydraulic cylinder.
Alternative designs of three-point linkages are known, such as the arrangements shown in U.S. Pat. No. 6,321,851, US2003/217852 and U.S. Pat. No. 5,997,024 in which the lower links are replaced by two, or four variable length hydraulic rams. This variable length ram arrangement enables multi axis movement of any implement attached to the linkage.
To control the three-point linkage, modern tractors are mainly equipped with electronic linkage control systems to improve work quality and operator comfort during operation.
Such electronic linkage control systems operate in three well known modes:
I) Position control mode: In general, the tractor speed is kept constant by a speed control system and the position of the lower lifting arms is sensed directly or indirectly so that the working depth of the implement in the soil can be adjusted within limits set by the operator whilst the speed of the tractor is kept constant. In the position control mode, the height of the linkage is determined by a function, H which relies solely on a height position component HP inputted or controlled by the tractor operator by means of, for example, a Depth Controller.
II) Draft control mode: The implement is raised and lowered in the soil automatically depending on the draft force applied by the implement to reduce fuel consumption, avoid engine stall or avoid damage of the implement or tractor. Again, vehicle speed is kept constant. If the implement is lowered into the ground an initial draft is applied defining a zero level. The operator can then set a value representing a force increase which means that the operator can decide how fast the implement is lifted when a small force increase or a large force increase occurs. The value of the force entered by the operator does not represent an exact value of the force applied, e.g. 5 kN, but defines the responsiveness of the draft control. The objective of this function is to move the implement while avoiding excessive draft or pull force variations. Therefore, a draft force sensor, typically in the form of a draft force sensing pin which connects the lower lifting arms to the tractor chassis is used to measure the horizontal load applied to the tractor by the implement. In the draft control mode, the height of the linkage is determined by a function, H which relies on a height draft component HD resulting from the draft force.
III) Intermix control mode: This control arrangement, as its name implies is a mixture of position and draft control modes in which a draft control system can only lift the implement within a limited range of positions. This function is provided to avoid excessive movement of the implement in the soil resulting in poor working quality. Again, vehicle speed is kept constant by a speed control system. In the intermix control mode, the height of the linkage is determined by a function H which relies on both the height draft component HD (from the draft mode) and the height position component HP (from the position control mode). A mix controller can vary the ratio of HD:HP and thus vary the influence from each of the position and draft control modes.
Only the draft control and intermix mode (both referred to as draft control modes) operate under measurement of the draft force. Generally, deactivating the draft modes results in that the system enters the position mode with no draft force influencing the lifting heights. It may, however be difficult to install a draft force sensing pin due to the complex three-dimensional geometry of a linkage.
The applicant's pending application WO2013/053645 describes an electronic linkage control wherein the draft force sensing pin is omitted and the variation of the draft force of the linkage is determined from the variation in the hydraulic drive circuit pressure. As described in WO2013/053645, such systems may also be used for implements which are simply towed by connection to e.g. a ball hitch, rather than being hitch-mounted. Different to fully-mounted implements the weight of the implement mainly rests on the ground via the implement wheels, and actuators are provided on the implements controlling the linkage thereon to raise and lower the soil-engaging means. The actuators, mainly hydraulic actuating cylinders similar to those used for three point linkages, are thereby supplied and controlled by the hydraulic supply system and valve arrangements of the tractor.
Furthermore, an implement may be semi-mounted, which means that the implement is mounted to the lower lifting arms of the tractor and further may be equipped with a ground engaging wheel so that the weight of the implement rests on the lower links and the ground via the implement wheels. To raise and lower the soil engaging means of the implement, the linkage of the tractor and the linkage of the implement must be adjusted conjointly.
Accordingly, the term “linkage” may be understood as not limited to a three-point linkage of a tractor, but may also include linkages to move soil-engaging means of towed implements.
Normally, in a draft control mode, the operator sets a value indicative of an acceptable draft force (depending on the condition of the ground and desired vehicle speed). If the draft force then increases continuously because a plough in the ground has hit a rock, the draft control will move the linkage upwards and therefore the plough will move upwards so that the draft force is reduced. If the draft force is reduced, the draft control mode will operate to lower the linkage and the plough towards the ground again. In this way, the plough will automatically pass a rock in the ground avoiding damage to it.
In addition to the automatic movement of the linkage in the draft control mode, the operator can also manually adjust the height of the linkage by using a Depth Controller in the cab.
Problems can arise with the linkage controls described above when an operator decelerates to a standstill with an implement attached. If an implement is being carried in a transport position (that is the linkage holds the implement so that it does not touch the ground) and the draft mode is not switched off, as the tractor is slowed down the linkage and implement is lowered. There is therefore a risk of damage to the implement, or uncoupling of the implement. The operator should lock the linkage, or switch to a positional mode to avoid such an event. This can be easily forgotten by an operator. Further, for the operator's comfort and economy of fuel, it is preferable for the vehicle to remain in the draft mode.
It is advantageous to have an automatic electronic linkage control which controls the height of the linkage of the tractor depending on the draft force. However, if no implement is attached, this function needs to be deactivated to avoid collision of the linkage with the ground or a tow bar. As a result, it is therefore necessary to detect whether an implement is attached to the linkage or not so that movement of the linkage by an automatic control can be prohibited, or permitted. If the implement is not fully-mounted to the three point hitch of the tractor but the position of the soil engaging means of implement may be controlled by draft force, the detection of the implement being trailed or semi-mounted may result in keeping the draft force active after confirmation by the operator.
A system may use a pressure sensor installed in the lifting cylinder of the linkage. For example, an unloaded linkage may result in the lifting cylinders indicating a pressure of 11 bar. When a plough is semi mounted that is, it is partly supported by the ground, the pressure may change to about 15 bar as the ground supports some of the weight of the plough. The difference therefore between the implement being semi mounted for operation and an unloaded linkage is around 4 bar which can be too small a change in pressure to detect. It can therefore be difficult for a system to recognise whether an implement is attached or not. When the plough is fully lifted into a transport position, or for rotation during a headland turn, the pressure will be greater than 25 bar which can be easily detected. However, during ploughing the external forces applied may result in the pressure in the cylinders detecting a pressure below 25 bar and the control system may register than no implement is attached. In such a situation, the draft control would be aborted by the control system and the position control mode activated. This leads to uncomfortable ploughing as the height of the linkage in the position control mode relies solely on a height position component HP of the linkage which is inputted, or controlled by the operator (instead of the height draft component HD resulting from the draft force as would be the case in the draft control mode).
Position sensors can be used to detect the position of an attached implement, or trailer to the linkage, but the position of the linkage does not indicate whether an implement is attached.
A tractor control unit may receive information by way of an ISOBUS system wherein an implement informs the tractor control unit of its attachment to the tractor. Alternatively an electric supply/light connector, or fluid couplings on the tractor to which the implement is attached may be used to detect the attachment of an implement. But these means do not provide information as to where the implement is attached, that is whether the implement is attached to the linkage or to a ball hitch, or at what height the implement is attached. Moreover, known systems do not automatically disengage the draft control mode as a tractor comes to a standstill, is driven at very low speeds under 1 kph, or is driven in reverse. Under these operating conditions, where the draft force drops, there is a danger of the implement being unintentionally lowered.